I found that the concentricity of the adapter hole and the cutout shape of the fork was not good. The cutout on the fork was not deep enough to accept the hub axle properly, causing the insertion of the thru axle to be very difficult. The adapter position had to be manually adjusted to ensure that the thru axle can pass through the adapter and hub axle smoothly.
While trying to solve this issue, I discovered something odd. There is a small bolt that fixes the Trail Mixer to the fork. Under the bolt head, there is also a small washer. As you can see from the pictures below, the washer will get deformed after the hub axle is installed. This condition applies to both sides of the Trail Mixer adapter.
Small washer under the bolt head gets deformed after wheel installation.
The edge of the washer is pressed down by the hub axle, which is odd since it seems to be a design mistake.
As you can see, the hub axle will press down on the edge of the washer once the thru axle is tightened.
Another view of this phenomenon.
The hub axle diameter is measured to be nominal, which is usually about 19 mm.
I have not encountered this problem before on my other thru axle bikes, like the Canyon Endurace or the Fabike C3. Of course those other bikes don't have the Trail Mixer adapter and thus no bolt or washer there.
This condition is unusual since I have not seen any design whereby the washer is designed to be deformed partially after installation. To me, it feels like there was not enough design clearance between the hub axle and the washer.
I first checked with the local bike dealer where I got the bike frame from, but they were unable to answer my question, although they did observe the same deformed washer phenomenon on their Aspero bikes. To them, it was not an issue, and suggested that I contact Cervelo directly if I have any doubts.
Which is exactly what I did, by sending in pictures of the deformed washers as you have seen above. The first reply that I got from Cervelo was that the official drawings of the bike does not have the washers included, although the product manual does have the washer.
Information from the Aspero product manual. The washer can be seen, but it is smaller than what I have on the actual bike.
What I found is that the product manual does show that it has washers, but they are smaller in diameter than what I have on the actual bike. The washer shown in the manual is the same size as the bolt head which would prevent it from being deformed by the hub axle.
Cervelo asked me to try installing the Trail Mixer bolts without the washer, to see if it fits better.
If the washers are included, the bolt length is perfectly flush with the outside of the Trail Mixer.
I removed the washers and tried to tighten the bolt, to fix the Trail Mixer to the fork.
However, due to the missing washer, the bolt will be too long and protrude from the outside of the Trail Mixer.
Also, if the washer is not used, tightening the bolt will cause the carbon surface on the fork to be damaged by the bolt head, as you can see from the depression formed.
Seems that a washer is necessary, in order to prevent damage to the fork during bolt tightening.
After some to and fro, and some discussion within Cervelo, the conclusion is that the washer is designed to be deformed, as per design intention. This is odd, but I accept their explanation even though I am not convinced. Anyway, it does not pose any safety issue and so I will not pursue further.
If you do notice it on your own Aspero, the official explanation from Cervelo is that the washer is meant to be deformed as per design intention.
Unfortunately that was not the only issue that I faced. The other issue was that during the fixing bolt tightening of the front brake adapter (shown below), the washer is too big (or adapter clearance too small). The effect is that when the bolt is being tightened, the washer will interfere with the adapter. The tightening action will also cause the adapter to move sideways, making it very difficult to set the brake caliper position accurately.
It took a lot of trial and error in order to fix the brake caliper position, so as to prevent rubbing with the disc brake rotor. This is another washer issue that I faced on this Aspero.
This problem came about because the brake adapter is a special one from Cervelo, which is designed for the Aspero. The brake adapter is needed when you use the rearward position of the Trail Mixer, which means that the brake caliper needs to be shifted more rearward to match the rearward position of the hub axle and disc rotor. If you use the forward position of the Trail Mixer, you will not encounter this issue.
I was told by Cervelo that the washer of the SRAM fixing bolt is smaller, and thus does not interfere with the brake adapter. I'm using the stock fixing bolt of the Dura-Ace R9170 brake caliper, which is what you see in the picture below. Apparently the washer of the Shimano fixing bolt is larger, which was not taken into account when Cervelo was designing the adapter.
Interference between the washer and the Aspero front brake adapter.
The reply from Cervelo was that they overlooked this, and they will ensure that the adapter works properly with standard fixing bolt and washers from major brake manufacturers, such as Shimano, SRAM, Campagnolo, etc. Good to know that they will make improvements to this.
In summary, I faced two washer problems with the Aspero, but luckily none of it was critical to safety or installation. I was glad that Cervelo was able to give me an answer, and that they are now aware of these issues, and will make improvements.